An arrangement for adjusting torque of an internal combustion engine which drives a change-speed gearbox with an automatic gear changing device whose power is controlled by an accelerator pedal operated by a driver. The power is controlled in dependence on stored characteristics with specified variation of a required torque value as a function of power demand, using switch-in signals which are derived from the gear changing device and which initiate switching of a stored characteristic into an adjustment element influencing the torque for controlling the adjustment element.
In a known arrangement of the above type shown in German Published Unexamined Patent Application No. 2,935,916, information is stored as a function of the current engine condition by a first characteristic field as a measure of the normal ignition point in time and the normal injection quantity necessary in the steady-state gear change condition.
Using a second characteristic field, information is provided as a measure of the particular reduction in the engine torque for each engine condition. An engagement signal supplied by a gearbox control unit initiates the gear change and determines the duration of the engine engagement for each engine condition, this engagement signal being preferably not of the same length for all gear change procedures.
An objective of the present invention is essentially to avoid, as far as possible, the driving instabilities, such as slip at the drive wheels when changing down gears or loss of drive torque when changing up gears, caused by the gear changing jolts which still occur during gear changes in the known arrangement. Those jolts occur because of the more or less abruptly changing torque curve, and hence, an objective of the present invention is to achieve better travelling comfort by avoiding driving instabilities.
This and other objectives are achieved in the present invention by providing an arrangement for adjusting torque of an engine which drives a change-gearbox with automatic gear changing device in dependence on stored characteristics with specified variation of a required torque value as a function of power demand, with at least two different gears each associated with an individual stored characteristic. Switching signals contain information on a gear to be selected. Engine power is at least approximately constant for each engine operating point in an engine characteristic field when changing between two associated stored characteristics for the required torque value. The adjustment element is controlled by the switched-in stored characteristic until the gear changing device switches to a gear having a different associated stored characteristic.
In the arrangement according to the present invention, the engine torque is fundamentally adjusted by gear-dependent characteristics which are graduated relative to one another so that the engine operating point moves along a line of approximately constant engine power in the engine characteristic field when changing to a different gear so that gear changing jolts and driving instabilities caused by the jolts no longer occur.
In certain advantageous embodiments of the present invention, each gear has its own characteristic for the required torque value allocated to it. Alternatively, one common characteristic is allocated to a plurality of gears.
For fixing the most favorable time for switching to the new characteristic for the required torque value during each gear change, in certain preferred embodiments, the arrangement comprises means for forming a switch-in signal dependent on a gear transmission ratio containing information on an actual value of the transmission ratio. Such an embodiment also includes means for associating the transmission ratio-dependent switch-in signal with a gear-dependent switch-in signal such that the characteristic for the required torque value is switched into the adjustment element approximately at a specified lead time before attainment of a required value of the gear transmission ratio associated with the gear to be selected.
When changing down, the time for switching in the new characteristic, associated with the lower gear, for the required torque value is fixed sufficiently late relative to the attainment of the new transmission ratio so that the gear change takes place rapidly with the higher power in the upper gear. At the same time, the transmission overshoot which is normally excited during changing down gears is damped or prevented. When changing up gears, on the other hand, it is advantageous to select a time lead for the switching points for changing over to the new required torque value characteristic associated with the higher gear. This is done so that by means of the increase in torque obtained by switching over the characteristics, a jolt-free transition during the transmission ratio-dependent change in torque is achieved.
The above aspects are taken into account in certain preferred embodiments of the present invention which include means for forming the time lead from a correction value associated with the required value of the gear transmission ratio. Further embodiments include variable delay means which receive the gear-dependent switch-in signal and are triggered by the transmission ratio-dependent switch-in signal. In certain embodiments, different correction values are used for changing up gears and changing down gears.
In certain preferred embodiments of the present invention, it has been found advantageous to the driving behavior of the vehicle to use characteristics in which the torque increases in the partial load range approximately linearly with the displacement of the accelerator pedal along the changing lines of the change-speed gearbox.
Certain advantageous embodiments include a switchable characteristic memory for storing the characteristics for the required torque value and identification transducer means controlled by the accelerator pedal which supplies a signal to the switchable characteristic memory. Also contemplated are embodiments having comparator means having an input, and gear change recognition means for alternatively connecting the input to a required value memory for the correction values during changing up gears and to a different required value memory for the correction values during changing down gears.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.